1. Field of the Invention
The present invention relates to an In-Plane Switching mode LCD (IPS-LCD) and, more particularly, to an electrode array structure of an IPS-LCD.
2. Description of the Related Art
Liquid crystal displays (LCDs) may be classified by the orientation of the liquid crystal molecules between the spaced apart substrates. In a conventional twisted nematic LCD (TN-LCD), the liquid crystal molecules are twisted between the two substrates. In contrast, in an in-plane switching mode LCD (IPS-LCD), common electrodes and pixel electrodes are formed on a lower glass substrate (TFT substrate) and an in-plane electric field therebetween is generated to rearrange the liquid crystal molecules along the in-plane electric field. Accordingly, the IPS-LCD has been used or suggested for improving viewing angle, contrast ratio and color shift.
In the IPS-LCD, the display characteristics of the view angle with respect to the invert luminance are superior. However, as shown in FIG. 1, when the liquid crystal molecules 1 are rotated to an angle 45xc2x0 with respect to the in-plane electric field, the observed image from the direction crossing at 45 degrees or 135 degrees against the lengthwise direction of the common electrodes 2 and the pixel electrodes 3 is colored blue or yellow. This is a problem to be solved in the image quality of the IPS-LCD.
Seeking to solve the coloring phenomenon, a herringbone-shaped electrode structure is developed for modifying the rotating angle of the liquid crystal molecules. As shown in FIG. 2, in the conventional IPS-LCD, a TFT substrate 10 has a plurality of parallel data lines 12 extending along Y-axis and a plurality of parallel gate lines 14 extending along X-axis, which are arranged in a manner to form a matrix of pixel areas 24. Also, a comb-shaped pixel electrode 18 and a herringbone-shaped common electrode 20 are disposed in each pixel area 24, and at least one TFT device 16 is disposed at a cross point of the data line 12 and the gate line 14. In addition, an orientation layer (not shown) is spread on the entire surface of the TFT substrate 10, and the orientation layer is rubbed in a direction shown by arrow A so as to make liquid crystal molecules 22 arrange along the direction A before an external voltage is applied to the TFT substrate 10.
The comb-shaped pixel electrode 18 has a bar 18a transversely disposed over the gate line 14 to form a capacitor, and a plurality of continuous saw-toothed teeth 18b, 18c extending along Y-axis from the bar 18a. The herringbone-shaped common electrode 20 has a center wiring portion 20a extending along X-axis, and a plurality of saw-toothed bones 20b, 20c bent at the center wiring portion 20a and respectively extending along a first Y-axis and a second Y-axis. For example, the bones 20b extending along the first Y-axis are parallel to the teeth 18b, 18c and the bones 20b arrange at intervals between the teeth 18b, 18c. 
When external voltage is applied to the TFT substrate 10, an in-plane electric field is formed between the bones 20a, 20b and the teeth 18b, 18c, resulting in a rotation of the liquid crystal molecules 22 toward the in-plane electric field. Using the center wiring portion 20a of the common electrode 20 as the discrimination, the pixel area 24 is divided into a first sub-pixel area 241 and a second sub-pixel area 242, and the liquid crystal molecules 22a and 22b positioned adjacent to the center wiring portion 20a respectively rotate in counterclockwise direction and in clockwise direction. In the first sub-pixel area 241, since the bones 20b, 20c and the teeth 18b, 18c have the same saw-toothed sidewalls, the liquid crystal molecules 22a and 22axe2x80x2 positioned adjacent to the tip of the saw-toothed sidewall respectively rotate in counterclockwise direction and in clockwise direction. Therefore, two domains are formed within the first sub-pixel area 241. Similarly, the liquid crystal molecules 22b and 22bxe2x80x2 also form two domains within the second sub-pixel area 242. Furthermore, the saw-toothed sidewalls lead to a specific tilted degree of the in-plane electric field which corresponds to the rotation angle of the major axes of the liquid crystal molecules 22. It is preferable that the rotation angle xcex8 of the liquid crystal molecules 22 satisfy the formula 0xc2x0 less than xcex8xe2x89xa6+60xc2x0 or xe2x88x9260xc2x0 xcex8 less than 0xc2x0 to solve the coloring phenomenon.
However, the liquid crystal molecules 22 positioned at the peaks of the saw-toothed sidewall, that is, the parting of the two domains of the sub-pixel area, are jostled by surrounding molecules 22 that rotate in a different direction, thus the liquid crystal molecules 22 on the parting of the two domains are stopped from rotating. Due to both the stopped rotation and the common electrode 20 and the pixel electrode 20 non-transparent nature, the liquid crystal molecules 22 positioned at the peaks of the saw-toothed sidewall present as dark lines after voltage is applied to the TFT substrate 10, as shown by dotted lies Ixe2x80x94I and IIxe2x80x94II. This decreases the aperture ratio of the IPS-LCD. Especially when the number of peaks of the saw-toothed sidewall is increased, the number of dark lines is correspondingly increased and thereby the aperture ratio is further decreased. Thus, a novel electrode array structure of the IPS-LCD eliminating the aforementioned problems is called for.
The present invention provides an electrode array structure to modify the rotation angle of the liquid crystal molecules, and achieve increased aperture ration and decreased driving voltage.
An electrode array structure in a pixel area of an in-plane switching mode LCD (IPS-LCD). A comb-shaped common electrode has a bar extending transversely and a plurality of teeth extending in a first lengthwise direction from the bar, in which each tooth of the common electrode has a continuous ∠-shaped sidewall. A comb-shaped pixel electrode has a bar extending transversely and a plurality of teeth extending in a second lengthwise direction from the bar, in which each tooth has a continuous ∠-shaped sidewall and parallel is disposed between adjacent teeth of the common electrode. An electric-field gradient is generated between the tooth of the common electrode and the adjacent tooth of the pixel electrode to form a non-uniform electric field.
Accordingly, it is a principle object of the invention to provide the ∠-shaped sidewall of the electrode to modify the rotation angle of liquid crystal molecules.
It is another object of the invention to make the rotation angle xcex8 of the liquid crystal molecules satisfy the formula 0xc2x0 less than xcex8xe2x89xa6+60xc2x0 or xe2x88x9260xc2x0xe2x89xa6xcex8 less than 0xc2x0.
Yet another object of the invention is to solve the coloring phenomenon.
It is a further object of the invention to increase the aperture ratio of the IPS-LCD.
Still another object of the invention is to provide an electric-field gradient between the tooth of the common electrode and the adjacent tooth of the pixel electrode to form a non-uniform electric field.
It is a further object of the invention to reduce the starting voltage, the driving voltage and the switching time of the IPS-LCD.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.